Premixing device for water heater and water heater having same

ABSTRACT

A premixing device for a water heater and the water heater having the same are provided. The premixing device for the water heater has a housing and a turning plate. A first airflow passage, a second airflow passage, a first gas passage and a second gas passage are formed in the housing. The turning plate is rotatably disposed on the housing to adjust an opening degree of the first gas passage and an opening degree of the first airflow passage. An air guide hole directly opposite to the first airflow passage is formed on the turning plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of International Application No. PCT/CN2022/109919 filed on Aug. 3, 2022, which claims priority to and benefits of Chinese Patent Application No.: 202121811940.0, filed on Aug. 4, 2021 and entitled “Premixing Device for Water Heater and Water Heater Having Same”, the entire contents of each of which are incorporated herein by reference for all purposes. No new matter has been introduced.

FIELD

The present disclosure relates to the field of domestic electrical appliances, and in particular, to a premixing device for a water heater and the water heater having same.

BACKGROUND

In the related art, a conventional combustion mode of a fully premixed condensing gas water heater needs to mix the gas and oxygen in advance and ensure that the air-fuel ratio is constant. The premixed gas and oxygen not only improve the combustion performance and but also produce a series of non-uniform air-fuel ratio problems, which have potential safety hazards. A mechanical premixer is widely used in the industry to mix gas and air in advance. However, the mechanical premixer cannot ensure that the air-fuel ratio is constant under conditions of small load and large load. In general, the mechanical premixer controls the air-fuel ratio through a turning plate, and the opening degree of the turning plate structure cannot effectively control the air-fuel ratio, especially under the condition of small load, since a part of the gas passages and airflow passages is completely closed by the turning plate, the air-fuel ratio of the water heater is too low under the condition of small load, leading to poor combustion performance and affecting the use of users, and even leading to a series of safety problems, such as, backfire and deflagration of the fully premixed gas water heaters.

SUMMARY

The present disclosure aims to solve at least one of the technical problems existing in the prior art.

To this end, in one embodiment of the present disclosure, a premixing device for a water heater and the water heater having same are proposed. The premixing device can ensure that the oxygen content of the entire load segment is constant, and the air-fuel ratio can be constant under both conditions of large load and small load. The premixing device has a simple structure and obvious effect, and can ensure good combustion performance and user safety.

In one embodiment of the present disclosure, a water heater with the premixing device as described above is proposed.

The premixing device for the water heater according to the present disclosure includes: a housing and a turning plate. A first airflow passage, a second airflow passage, a first gas passage and a second gas passage are formed in the housing. The turning plate is rotatably disposed on the housing to adjust an opening degree of the first gas passage and an opening degree of the first airflow passage, and an air guide hole directly opposite to the first airflow passage is formed on the turning plate.

The present disclosure uses a turning plate structure to control the gas flow, and the turning plate can solve the problem of a low oxygen content of the fully premixed gas water heater under the condition of small load operation by adjusting the gas flow area between the first airflow passage and the first gas passage, to ensure that the oxygen content of the entire load segment is constant, and to achieve the purpose of a constant air-fuel ratio. This arrangement has a simple structure and obvious effect, and can ensure good combustion performance and user safety.

According to one example of the present disclosure, the first gas passage is surrounded by the first airflow passage.

According to one example of the present disclosure, a first support portion is disposed in the housing, and the first airflow passage is formed in the first support portion. A second support portion is disposed in the first airflow passage, and the first gas passage is formed in the second support portion.

According to one example of the present disclosure, an end surface of the free end of the second support portion and an end surface of the free end of the first support portion are disposed obliquely, and the turning plate is rotatable to abut against the end surface of the second support portion and/or the end surface of the first support portion.

According to one example of the present disclosure, the first support portion is inclined towards the direction of air flow from top to bottom.

According to one example of the present disclosure, a third support portion is disposed in the housing, and a second airflow passage is formed in the third support portion. A fourth support portion is disposed in the second airflow passage, and a second gas passage is formed in the fourth support portion. An end surface of the third support portion protrudes relative to an end surface of the first support portion.

According to one example of the present disclosure, a first support rib is disposed between the first support portion and the second support portion, and a second support rib is disposed between the third support portion and the fourth support portion.

According to one example of the present disclosure, a deflector rib directly opposite to the first gas passage is formed on the turning plate.

According to one example of the present disclosure, the sectional area of the second gas passage is smaller than the sectional area of the first gas passage.

The water heater according to the present disclosure is briefly described below.

The water heater according to the present disclosure is provided with the premixing device according to the above-mentioned embodiments, and since the water heater according to the present disclosure is provided with the premixing device according to any one of the above-mentioned examples, the water heater has a turning plate structure, which can ensure that the air-fuel ratio is constant under the condition of small load. Such arrangement has good combustion performance, safe use, a simple structure and convenient installation.

Additional aspects and advantages of the present disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and/or additional aspects and advantages of the present disclosure will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a sectional view of a premixing device according to embodiments of the present disclosure.

FIG. 2 is a rear view of a premixing device according to embodiments of the present disclosure.

FIG. 3 is a schematic diagram of a premixer gas air flow passage according to embodiments of the present disclosure.

REFERENCE NUMERALS

-   -   premixing device 1;     -   housing 10;     -   first support portion 11; second support portion 12; third         support portion 13; fourth support portion 14;     -   first airflow passage 11 a; first gas passage 12 a; second         airflow passage 13 a; second gas passage 14 a;     -   turning plate 20;     -   air guide hole 21; and deflector rib 22.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. Embodiments described below with reference to the accompanying drawings are exemplary and are intended to be illustrative of the present disclosure and are not to be construed as limiting the present disclosure.

In the related art, a conventional combustion mode of a fully premixed condensing gas water heater needs to mix the gas and oxygen in advance and ensure that the air-fuel ratio is constant. The premixed gas and oxygen not only improve the combustion performance and but also produce a series of non-uniform air-fuel ratio problems, which have potential safety hazards. A mechanical premixer is widely used in the industry to mix gas and air in advance. However, the mechanical premixer cannot ensure that the air-fuel ratio is constant under conditions of small load and large load. In general, the mechanical premixer controls the air-fuel ratio through a turning plate, and the opening degree of the turning plate structure cannot effectively control the air-fuel ratio, especially under the condition of small load, since apart of the gas passages and airflow passages is completely closed by the turning plate, the air-fuel ratio of the water heater under the condition of small load is too low, leading to poor combustion performance and affecting the use of users, and even leading to a series of safety problems, such as, backfire and deflagration of the fully premixed gas water heaters.

A premixing device for a water heater according to embodiments of the present disclosure is described below with reference to FIGS. 1-2 .

As shown in FIGS. 1-2 , the premixing device 1 for the water heater according to the present disclosure includes a housing 10 and a turning plate 20. A first airflow passage 11 a, a first gas passage 12 a, a second airflow passage 13 a, and a second gas passage 14 a are formed in the housing 10. Air may enter the housing 10 via the first airflow passage 11 a and the second airflow passage 13 a, and gas may enter the housing 10 via the first gas passage 12 a and the second gas passage 14 a. The turning plate 20 is disposed on the housing 10, and can rotate on the housing 10. The turning plate 20 limits the gas flow passing through the first gas passage 12 a by adjusting an opening degree of the first gas passage 12 a and an opening degree of the first airflow passage 11 a. An air guide hole 21 is formed on the turning plate 20, and is directly opposite to the first airflow passage 11 a. Air may pass through the air guide hole 21, and the turning plate 20 can obstruct the gas flow and prevent the gas flow passing through the turning plate 20 from being excessive.

The premixing device 1 of the present disclosure is used in a gas water heater. After the premixing device 1 of the present disclosure and a fan of the water heater are installed, gas and air respectively enter the premixing device 1 for premixing. The gas enters the first gas passage 12 a and the second gas passage 14 a, and the air also enters the first airflow passage 11 a and the second airflow passage 13 a. Under the condition of maximum load operation, the turning plate 20 is fully opened due to the attraction of the fan, the first gas passage 12 a and the second gas passage 14 a are simultaneously conducted to provide gas, the first airflow passage 11 a and the second airflow passage 13 a are simultaneously conducted to provide air, and the air is mixed with the gas. Under the condition of minimum load operation, the opening degree of the turning plate 20 is reduced, and the flow of the first gas passage 12 a and the flow of the first airflow passage 11 a are small. The gas flow passing through the first gas passage 12 a is small, and at this time, the turning plate 20 almost completely falls down, blocks the gas flow, and limits the gas from entering the mixture gas cavity through the first gas passage 12 a. The air can also pass through the turning plate 20 from the air guide hole 21 directly opposite to the first airflow passage 11 a on the turning plate 20, so that under the condition of small load operation, the airflow passing through the second airflow passage 13 a and the airflow passing through the air guide hole 21 on the turning plate 20 simultaneously provide air. Due to the arrangement of the air guide hole 21, the premixing device 1 of the present disclosure may reduce the gas flow and increase the airflow simultaneously under the condition of small load, which increases the air-fuel ratio of the premixing device 1 under the condition of small load, ensures the use safety of the gas water heater, and improves the combustion performance of the gas water heater.

In the premixing device 1 according to the present disclosure, the turning plate 20 may be rotated under an airflow driven by the fan of the water heater. After the diameters of the first gas passage 12 a and the second gas passage 14 a are determined, at a low rotation speed of the fan, the turning plate 20 will close the first airflow passage 11 a and the first gas passage 12 a, and the air-fuel ratio flowing through the second gas passage 14 a and the second airflow passage 13 a is constant, and the air supplied by using only the second airflow passage 13 a cannot reach a preset air-fuel ratio, so the air flow needs to be increased. In this scheme, the method of opening a hole on the turning plate 20 is adopted to increase the air flow under the condition of small load, so as to increase the air-fuel ratio under the condition of small load. The turning plate 20 can adjust the airflow area of the first airflow passage 11 a and the airflow area of the first gas passage 12 a to solve the problem of low oxygen content of the fully premixed gas water heater under the condition of small load, thereby ensuring that the oxygen content of the entire load segment is constant and achieving the purpose of a constant air-fuel ratio. This arrangement has a simple structure and obvious effect, and can ensure good combustion performance and user safety.

In some embodiments of the present disclosure, the housing 10 is divided into an upper housing and a lower housing. A gas inlet and an air inlet are distributed on the upper housing. A first airflow passage 11 a, a second airflow passage 13 a, a first gas passage 12 a and a second gas passage 14 a are formed in the lower housing. The gas enters the cavity of the first gas passage 12 a through the gas inlet of the upper housing, and the air enters the first airflow passage 11 a through the air inlet of the upper housing. The first gas passage 12 a is surrounded by the first airflow passage 11 a, the first airflow passage 11 a is formed around the outer periphery of the first gas passage 12 a, the gas diverges to the outer periphery from the middle part of the air, and the gas can be fully dispersed and mixed in the airflow. Thus, the mixing of the gas and air is more uniform, and the possibility of deflagration is reduced, and thus the gas can be fully mixed, and the mixing effect is good, which ensures that the water heater can have a good combustion performance.

In some embodiments of the present disclosure, a first support portion 11 is disposed in the lower housing, and defines a first airflow passage 11 a. A second support portion 12 is disposed in the first airflow passage 11 a, and defines a first gas passage 12 a. The first support portion 11 and the second support portion 12 may be integrally formed with the housing 10 respectively, or the first support portion 11 and the second support portion 12 may be constructed as an integral injection-molded piece with the housing 10. The arrangement of the first support portion 11 and the second support portion 12 is used to form a first gas passage 12 a and a first airflow passage 11 a, and the arrangement of the first airflow passage 11 a surrounding the first gas passage 12 a is achieved by arranging the second support portion 12 in the first airflow passage 11 a of the first support portion 11.

In other embodiments of the present disclosure, the first support portion 11 and the second support portion 12 are juxtaposed, such that the first airflow passage 11 a and the first gas passage 12 a are spaced apart from each other, and the first airflow passage 11 a and the first gas passage 12 a are parallel to each other.

In some embodiments of the present disclosure, the second support portion 12 located on the lower housing has two end surfaces, the end surface in contact with the upper housing is an end surface of a non-free end, and the other end surface of the second support portion 12 is a free end. The first support portion 11 located on the lower housing has two end surfaces, the end surface in contact with the upper housing is an end surface of a non-free end, and the other end of the first support portion 11 is a free end. The end surface of the free end of the second support portion 12 and the end surface of the free end of the first support portion 11 are disposed obliquely. The turning plate 20 can rotate to abut against the end surface of the second support portion 12 and/or the end surface of the first support portion 11. Under the condition of small load, the fan of the water heater cannot drive the turning plate 20, and the turning plate 20 abuts against the end surface of the second support portion 12 and the end surface of the first support portion 11 under the action of its own gravity, thereby closing the first gas passage 12 a and the first airflow passage 11 a, to adapt to the small load condition of the water heater.

In some embodiments of the present disclosure, the end surface of the free end of the first support portion 11 located on the lower housing is inclined towards to the direction of air flow from top to bottom, and the turning plate 20 is installed on the end surface of the free end of the first support portion 11. Since the end surface of the free end of the first support portion 11 is disposed obliquely, the turning plate 20 can generate a component force pressed against the end surface of the free end of the first support portion 11 under the action of gravity, so that the turning plate 20 stably closes in front of the first airflow passage 11 a and the first gas passage 12 a. After the fan is turned on, the attraction force of the fan may make the turning plate 20 open, the air in the first airflow passage 11 a and the gas in the first gas passage 12 a can pass through the baffle plate, and by changing the load when the fan is operated, the opening degree of the turning plate 20 can be controlled, thereby controlling the gas flow passing through the first gas passage 12 a.

By obliquely arranging the end surface of the free end of the first support portion 11 and the end surface of the free end of the second support portion 12, the gravity of the turning plate 20 generates a component force on the end surface of the first support portion 11 and the end surface of the second support portion 12 so that the turning plate 20 is pressed against the end surface of the free end of the first support portion 11 and the end surface of the free end of the second support portion 12, thereby effectively closing the first gas passage 12 a and the first airflow passage 11 a.

In some embodiments of the present disclosure, a third support portion 13 is disposed in the lower housing, and defines a second airflow passage 13 a. A fourth support portion 14 is disposed in the second airflow passage 13 a, and defines a second gas passage 14 a. An end surface of the third support portion 13 is provided protruding relative to an end surface of the first support portion 11. The third support portion 13 and the fourth support portion 14 may be integrally formed with the housing 10 respectively, and the third support portion 13 and the fourth support portion 14 may be constructed as an integral injection-molded piece with the housing 10. The arrangement of the third support portion 13 and the fourth support portion 14 is used to form a second gas passage 14 a and a second airflow passage 13 a. The arrangement of the second airflow passage 13 a surrounding the second gas passage 14 a is achieved by arranging the fourth support portion 14 in the second airflow passage 13 a of the third support portion 13. In other embodiments of the present disclosure, the third support portion 13 and the fourth support portion 14 are juxtaposed such that the second airflow passage and the second gas passage are spaced apart from each other, and the second airflow passage and the second gas passage are parallel to each other.

In some embodiments of the present disclosure, a first support rib is disposed between the first support portion 11 and the second support portion 12, and is used for connecting the inner peripheral wall of the first airflow passage 11 a and the outer peripheral wall of the second support portion 12, which improves the stability of the second support portion 12 and ensures that the entire structure of the premixing device 1 is reliable. The first support rib may be configured in a plurality, and a plurality of first support members are spaced apart and disposed around the outer periphery of the second support portion 12.

The second support rib is disposed obliquely near one end of the turning plate 20 and is disposed between the third support portion 13 and the fourth support portion 14. The second support rib is used for connecting the inner side wall of the second airflow passage 13 a and the outer peripheral wall of the fourth support portion 14 to support the fourth support portion 14. The stability of the fourth support portion 14 is improved and the reliability of the entire structure of the premixing device 1 is ensured. The second support rib may be configured in a plurality, and a plurality of second support ribs are spaced apart and disposed around the outer periphery of the fourth support portion 14. In some embodiments of the present disclosure, the turning plate 20 is provided with a deflector rib 22 directly opposite to the first gas passage 12 a, and the deflector rib 22 is in an arc shape. Two ends of the arc-shaped deflector rib 22 are free ends, the arc-shaped opening of the deflector rib 22 faces one side of the pivot shaft of the turning plate 20, and the height of the deflector rib 22 gradually decreases from the middle to the direction of the free end.

Under the condition that the turning plate 20 opens the first gas passage 12 a and the first airflow passage 11 a with a small opening degree, the flow rate of the gas is too large, and the air-fuel ratio cannot meet the design requirements, and the deflector rib 22 can reduce the flow rate of the gas in the corresponding first gas passage 12 a and reduce the gas flow, so that the mixed gas reaches a preset air-fuel ratio.

In some embodiments of the present disclosure, the sectional area of the first gas passage 12 a is greater than the sectional area of the second gas passage 14 a. In the process that the turning plate 20 gradually opens the first gas passage 12 a, the premixing device 1 switches from the condition of the small load to the condition of the large load, and the cross sectional area of the first gas passage 12 a is greater than the cross sectional area of the second gas passage 14 a, which achieves the gas demand of the water heater for a large load. According to an exemplary embodiment of the present disclosure, the premixing device 1 for the water heater includes a housing 10 and a turning plate 20. The housing 10 includes an upper housing and a lower housing. The upper housing has gas inlets and air inlets which do not communicate with each other, and the lower housing is provided with a first support portion 11 and a third support portion 13. The first support portion 11 defines a first airflow passage 11 a, and the third support portion 13 defines a second airflow passage 13 a. A second support portion 12 is disposed in the first airflow passage 11 a, and a fourth support portion 14 is disposed in the second airflow passage 13 a. The second support portion 12 defining a first gas passage 12 a, and the fourth support portion 14 defining a second gas passage 14 a. A first support rib is disposed on the inner peripheral wall of the first airflow passage 11 a in the first support portion 11, and the first support rib connects the first support portion 11 and the second support portion 12. A second support rib is disposed on the inner wall of the second airflow passage 13 a in the third support portion 13, and the second support member connects the third support portion 13 and the fourth support portion 14. The gas inlets on the upper housing is in communication with the second support portion 12 and the fourth support portion 14, respectively; and the gas enters the gas inlets of the housing 10 and then enters the first gas passage 12 a and the second gas passage 14 a, respectively. The air enters the air inlets of the housing 10 and then enters the first airflow passage 11 a and the second airflow passage 13 a, respectively.

A turning plate 20 is disposed on the lower housing, the turning plate 20 is located on a side of the lower housing away from the upper housing, a mounting groove is disposed on a side wall of the lower housing directly opposite to each other, a pivot shaft is disposed in the mounting groove, and the turning plate 20 is connected to the pivot shaft to be rotatably disposed on the lower housing.

The first support portion 11 and the second support portion 12 of the housing 10 respectively have two end surfaces, the end surface away from the upper housing is a free end, and the end surfaces of two free ends are disposed obliquely towards the direction of air flow from top to bottom. The turning plate 20 can rotate to abut against the end surface of the first support portion 11 and/or the end surface of the second support portion 12, and the turning plate 20 can stably close the first airflow passage 11 a and the first gas passage 12 a under the action of gravity. Two air guide holes 21 are formed on the turning plate 20, and the air guide holes 21 are formed directly opposite to the first airflow passage 11 a. A deflector rib 22 is disposed on the turning plate 20, the deflector rib 22 is directly opposite to the first gas passage 12 a, the deflector rib 22 is in an arc shape, two ends of the deflector rib 22 are free ends, the arc-shaped opening of the deflector rib 22 faces the direction of air circulation, and the height of the deflector rib 22 gradually decreases towards the direction of the free end.

After the premixing device 1 for the water heater of the present disclosure and the fan of the water heater are installed, air enters the first airflow passage 11 a and the second airflow passage 13 a respectively from the air inlet of the upper housing, and gas enters the first gas passage 12 a and the second gas passage 14 a respectively from the gas inlet of the upper housing. Under the condition of maximum load operation, since the turning plate 20 is fully opened under the attraction force of the fan, the gas can be mixed through the first gas passage 12 a and the second gas passage 14 a and the air entering the first airflow passage 11 a and the second airflow passage 13 a, to ensure the content of air and gas in the mixed gas. Under the condition of minimum load operation, the gas flow passing through the first gas passage 12 a is small, and at this time, the turning plate 20 almost completely falls down, the turning plate 20 limits the gas flow in the first gas passage 12 a, and the air in the first airflow passage 11 a can pass through the air guide hole 21 on the turning plate 20, so that the air-fuel ratio can be controlled while reducing the gas flow, ensuring safe use and good combustion performance.

The premixing device 1 for the water heater of the present disclosure has a simple structure and can achieve the purpose of constant air-fuel ratio from a small load segment to a large load segment by adjusting the flow area of an airflow passage, and such a preheating device has good combustion performance, safe use, a simple structure and convenient installation.

The water heater according to the present disclosure is briefly described below.

The water heater according to the present disclosure is provided with the premixing device 1 of the above-mentioned embodiments, and since the water heater according to the present disclosure is provided with the premixing device 1 according to any one of the above-mentioned embodiments, the water heater has a turning plate 20, which can ensure that the air-fuel ratio is constant under the condition of small load, and such arrangement has good combustion performance, safe use, a simple structure and convenient installation.

In the description of the present disclosure, it should be understood that the terms “middle”, “longitudinal”, “transverse”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, and the like designate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing and simplifying the description, not intended or suggested that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the disclosure.

In the description of the present disclosure, “a first feature” and “a second feature” may include one or more of the features.

In the description of the present disclosure, “a plurality of” means two or more.

In the description of the present disclosure, a first feature being “above” or “below” a second feature may include that the first and second features are in direct contact, or the first and second features are not in direct contact but are in contact through additional features between them.

In the description of the present disclosure, a first feature being “over”, “above” and “on” a second feature includes the first feature being directly above and obliquely above the second feature, or merely means that the first feature is at a higher level than the second feature.

In the description of the present specification, references to descriptions of the terms “one embodiment”, “some embodiments”, “examples”, “specific examples”, or “some examples”, etc. mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, incorporation and combination of the various embodiments or examples and features of the various embodiments or examples described in this specification may be made by those skilled in the art without conflicting with each other.

While embodiments of the present disclosure have been shown and described, it will be understood that the above-described embodiments are illustrative and are not to be construed as limiting the present disclosure, and that variations, modifications, substitutions, and alterations in the above-described embodiments may be affected by one of ordinary skill in the art without departing from the scope of the present disclosure. 

What is claimed is:
 1. A premixing device for a water heater, the premixing device comprising: a housing, in which a first airflow passage, a second airflow passage, a first gas passage, and a second gas passage are formed; and a turning plate rotatably disposed on the housing to adjust an opening degree of the first gas passage and an opening degree of the first airflow passage, an air guide hole directly opposite to the first airflow passage being formed on the turning plate.
 2. The premixing device for the water heater according to claim 1, wherein the first gas passage is surrounded by the first airflow passage.
 3. The premixing device for the water heater according to claim 2, wherein: a first support portion is disposed in the housing, the first airflow passage being formed in the first support portion; and a second support portion is disposed in the first airflow passage, the first gas passage being formed in the second support portion.
 4. The premixing device for the water heater according to claim 3, wherein: an end surface of a free end of the second support portion and an end surface of a free end of the first support portion are disposed obliquely; and the turning plate is rotatable to abut against the end surface of the second support portion and/or the end surface of the first support portion.
 5. The premixing device for the water heater according to claim 4, wherein the first support portion is inclined in an air flow direction from top to bottom.
 6. The premixing device for the water heater according to claim 4, wherein: a third support portion is disposed in the housing, a second airflow passage being formed in the third support portion; a fourth support portion is disposed in the second airflow passage, a second gas passage being formed in the fourth support portion; and an end surface of the third support portion protrudes relative to the end surface of the first support portion.
 7. The premixing device for the water heater according to claim 6, wherein: a first support rib is disposed between the first support portion and the second support portion; and a second support rib is disposed between the third support portion and the fourth support portion.
 8. The premixing device for the water heater according to claim 5, wherein: a third support portion is disposed in the housing, a second airflow passage being formed in the third support portion; a fourth support portion is disposed in the second airflow passage, a second gas passage being formed in the fourth support portion; and an end surface of the third support portion protrudes relative to the end surface of the first support portion.
 9. The premixing device for the water heater according to claim 8, wherein: a first support rib is disposed between the first support portion and the second support portion; and a second support rib is disposed between the third support portion and the fourth support portion.
 10. The premixing device for the water heater according to claim 1, further comprising a deflector rib directly opposite to the first gas passage, wherein the deflector rib is disposed on the turning plate.
 11. The premixing device for the water heater according to claim 1, wherein a sectional area of the second gas passage is smaller than a sectional area of the first gas passage.
 12. A water heater, comprising a premixing device, the premixing device comprising: a housing, in which a first airflow passage, a second airflow passage, a first gas passage, and a second gas passage are formed; and a turning plate rotatably disposed on the housing to adjust an opening degree of the first gas passage and an opening degree of the first airflow passage, an air guide hole directly opposite to the first airflow passage being formed on the turning plate.
 13. The water heater according to claim 12, wherein the first gas passage is surrounded by the first airflow passage.
 14. The water heater according to claim 13, wherein: a first support portion is disposed in the housing, the first airflow passage being formed in the first support portion; and a second support portion is disposed in the first airflow passage, the first gas passage being formed in the second support portion.
 15. The water heater according to claim 14, wherein: an end surface of a free end of the second support portion and an end surface of a free end of the first support portion are disposed obliquely; and the turning plate is rotatable to abut against the end surface of the second support portion and/or the end surface of the first support portion.
 16. The water heater according to claim 15, wherein the first support portion is inclined in an air flow direction from top to bottom.
 17. The water heater according to claim 15, wherein: a third support portion is disposed in the housing, a second airflow passage being formed in the third support portion; a fourth support portion is disposed in the second airflow passage, a second gas passage being formed in the fourth support portion; and an end surface of the third support portion protrudes relative to the end surface of the first support portion.
 18. The water heater according to claim 17, wherein: a first support rib is disposed between the first support portion and the second support portion; and a second support rib is disposed between the third support portion and the fourth support portion.
 19. The water heater according to claim 16, wherein: a third support portion is disposed in the housing, a second airflow passage being formed in the third support portion; a fourth support portion is disposed in the second airflow passage, a second gas passage being formed in the fourth support portion; and an end surface of the third support portion protrudes relative to the end surface of the first support portion.
 20. The water heater according to claim 19, wherein: a first support rib is disposed between the first support portion and the second support portion; and a second support rib is disposed between the third support portion and the fourth support portion. 